Micro-cogeneration system: how to produce electricity and thermal energy in the house
With the term Cogeneration it refers to the practice of producing a combined manner in electrical and thermal energy, with the aim of obtaining a primary energy consumption lower than consumption that would occur with the separate production of the two energies.
Clearly the combined production of energy has meaning where there is a need for both energy supply, and in such contexts, the CHP solution can be a viable solution for energy and cost savings.
The cogeneration plant is obtained by using a heat engine capable of converting the energy released by combustion into mechanical energy (and from this into electrical energy), and to generate heat energy recovery as "waste" in the previous process.
An example of energy "recoverable" you can have immediate reflecting thermal energy dissipated in an internal combustion engine, since not required for the purposes of the useful effect of the engine, as well as a "potential is not exploited" for the first process consists in the direct production of heat energy in a gas boiler, without production of electrical energy, energy that would have been possible to generate from the gas by means of a heat engine which would have been recovered from the thermal energy "waste".
In order for the CHP to be attractive compared to separate production of the two forms of energy, it is necessary that the consumption of energy by cogeneration is less than the sum of consumption for separate production.
In reality, there are special indices, but their exposure would make the speech unnecessarily technicist for exposure of this solution.
RECOVERY OF WASTE AND SCENARIO OF USE
One can evaluate the magnitude of the thermal energy recoverable from an internal combustion engine by the following picture:
Referring to 100% of the chemical energy contained in the fuel (and bearing in mind that these are general data), it can be noted that:
or slightly more than 40% of the energy can be transformed into mechanical
or thermal energy "waste" amounts to about 58%
The subsequent conversion of mechanical energy into electrical and thermal energy recovery are in turn linked to the returns processing required to be submitted, and this leads to an estimated loss of about 10%, with a final condition which provides :
Electricity or recoverable net: 40%
or Losses: 10%
or Heat: 50%
Now, let's assume a case of home run, without even entering the implementations of the various companies of devices for CHP production.
Consider an apartment with an electrical output of 4kW committed and a request for thermal power of 5kW, remembering that a course based reasoning powers can be misleading as it would be appropriate to speak of energy, but in the first analysis can be, albeit simplistic, useful to understand the benefits that could be obtained.
Referring to the values displayed for the internal combustion engine and made 100 chemical energy introduced with the fuel, according to the conversion percentages indicated there would 40 units of electricity and 50 of thermal energy in the form of recovered heat.
Referring therefore to 10kW of "power fuel" (the quotation marks indicate the apparent imprecision want to reference in terms of power of the fuel, but as mentioned in the introduction above, useful for the purposes of argument) you would get the perfect meeting energy requirements.
Now compare with separate consumption:
4kW or absorbed by the network, products with an average yield of 50% (value quite high compared to the average of the network)
5kW or produced by a domestic gas boiler with an efficiency of 90% (flying on speech, "condensation", addressed in two previous posts 1 and 2)
Referring to the primary energy source and performing the calculations, we obtain:
or need to 8kW for electricity production
or need to 5.56kW for heat production
Altogether serve 13.56kW referring to the primary energy for the separate production, compared to 10 kW for the production cogeneration.
Bearing in mind that in such treatment there are several inaccuracies both in terms "quantitative" (eg on the thermal and electrical properties required for an apartment) that "qualitative" (for the need to refer to the energy and not to the power, while taking in account the importance of this, especially in terms of maximum power for the plant) and recalling that its purpose was to make evident the convenience of cogeneration in the contexts in which it is possible to
MICRO AND TRIGENERATION
The co-generation through the use of gas turbines and internal combustion engines can be applied in many scenarios in which the electrical and thermal demand levels are not high compared to the industrial sector, such as hotel facilities, sports centers, buildings used for offices in which the power consumption does not reach high levels while the demand for thermal energy becomes especially that for uses thermal-health.
In the case in which the cogeneration plant allows to follow the real power demand (especially electricity) user you have a function that interferes little with the national grid, while in the case where it is necessary to integrate or transfer energy from the network becomes necessary, in case of strong diffusion of distributed generation, the adoption of a transport network of type "intelligent" (Smart Grid), which is able to operate with no more than a few production points but with many of these, and this issue is much debated because of the problems to be overcome for its efficient and reliable management.
It 'also possible to assume a scenario of use restricted to single housing complexes, where replacement of the boiler for central heating with a cogeneration unit of small power (almost exclusively an internal combustion engine, as the solution represented in the following image to title for example) that produces the electrical power to the various users and the heat for heating:
As an example, we can assume a building with 40 apartments and a power supply unit equal to the supply of standard residential ENEL 3kW.
The required electric power cogeneration unit will therefore be 3kW • 40 = 120kW electric.
Such electric power is about 40% of the total power of the fuel, of which approximately 10% is lost due to irreversibility mechanical (friction) and the remaining 50% in the form of heat, therefore has available a potential of about 150kW heat that can be recovered (of course with due efficiency) for the uses thermal-health of the building.
Due to the seasonality of the thermal demand for this type of user, it is evident that this solution can become uneconomical during the months in which you do not work the thermal recovery.
One way to overcome this problem is the use of absorption refrigeration systems that, by using the heat produced by the plant, they can operate the air conditioning of the users, so we can talk trigeneration, or combined production of electricity, heat and " Cooling, "according to the following scheme:
Obviously, in a residential setting it clashes with management problems "condominium" it would be too difficult to use these solutions, but within structures designed for offices (think eg to banks), this solution is more manageable and feasible.
CO-GENERATION: THE FUTURE
And 'quite realistic to assume a development of cogeneration plants especially with regard to reduced power, while for the technology to be adopted can be considered as fuel cells, in addition to their introduction for electricity production, will receive a significant boost also for the production of thermal energy, while proven technologies, will continue on the path of technological improvement.
07/03/2011
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Translated via software
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Source:
Italian version of ReteIngegneri.it